With bombing suspect caught, question now is why?

Items and crosses decorate a makeshift memorial Saturday on Boylston Street, near the scene of Boston Marathon explosions, the morning after after the capture of the second of two suspects wanted in the Boston Marathon bombings.(Photo: Timothy A. Clary, AFP/Getty Images)

With Friday's dramatic capture of Dzhokhar Tsarnaev, federal investigators have a rare chance to gather firsthand information to determine whether the deadly Boston Marathon bombings are an isolated attack or part of a broader initiative of homegrown or international terrorism.

Tsarnaev, 19, remains hospitalized, listed in serious condition with gunshot wounds. He faces a number of potential charges ranging from murder and terrorism to manufacturing bombs.

Officials say a special interrogation team for high-value suspects plans to question him without reading him his Miranda rights, invoking a rare public safety exception triggered by the need to protect police and the public from immediate danger.

Tsarnaev's arrest and earlier killing of older brother Tamarlan Tsarnaev, 26, eased five days of tension and anxiety for much of the country, with a celebratory mood especially strong in Boston. The city's beloved Red Sox postponed Friday's game. When the team took the field at Fenway Park Saturday, the players' uniforms had "Boston" stitched on the front instead of the customary "Red Sox." The word "strong" adorned the Park's famed green centerfield wall.

As Boston rallies and recovers, about 50 of the 180 wounded in Monday's bombing remain hospitalized, with three still in critical condition.

President Obama vowed investigators will determine the cause of the attacks and whether there was outside help. "The families of those killed so senselessly deserve answers," he said.

FBI Director Robert Mueller said the investigation is ongoing and focused on learning as much as they can from Dzhokhar Tsarnaev. An FBI crisis negotiator spoke with Dzhokhar for about 25 minutes last night before he climbed out of the trailered boat he was hiding in behind a Watertown home and gave himself up. It is not known what, if anything, Dzhokhar said about Monday's bombings.

Tsarnaev and his family are ethnic Chechens from southern Russia who arrived in the USA in 2002 or 2003 and lived in the Boston area.

The FBI had Tamerlan Tsarnaev on its radar in early 2011, when Russia requested information about him. The request was based on the information that the former Golden Gloves boxer had become a follower of radical Islam and a "strong believer,'' according to the FBI. The request suggested Tsarnaev was traveling overseas to join "unspecified underground groups."

A federal law enforcement official said Saturday that FBI agents conducted a review of Tamerlan Tsarnaev's activities and possible links to radical Islam and Chechen extremists for about two months prior to the suspect's six-month trip to Russia in 2012.

The official, who is not authorized to comment publicly, said the Russian government requested the FBI's assistance as part of the foreign police cooperation program.

Under the program, the FBI provides investigative assistance to other governments when they have concerns about the activities of U.S. citizens related to travel, communications or associations in those countries. The FBI, the official said, responds to "thousands'' of such requests each year. And other governments provide the same service to the FBI.

In the Tsarnaev case, the official said agents checked U.S. databases, communications records, contacts with Internet websites and other activities.

Tsarnaev and his parents also submitted to voluntary interviews, which the official described as "very cooperative.''

"Nothing emerged that concerned us,'' the official said. "There just wasn't anything there. We ask that the government get back with us if they develop new information, but they did not. The Russians seemed satisfied, so we closed it.

"We didn't find anything at all that came back interesting. There was no evidence of any mischief,'' the official said.

Tasarnaev returned on July 7, 2012, but Russian authorities never asked for additional assistance, nor did they share information about his travels there.

As part of the investigation, the official said agents will be seeking further information about the Russian's initial interest.

"The best part of this is that the kid is alive,'' the official said, indicating that investigators hope the surviving younger suspect could provide more information about contacts or assistance the brothers may have allegedly received in carrying out the attacks.

Tasarnaev had strong political views about the U.S., according to Albrecht Ammon, 18, a Cambridge, Mass., neighbor. Ammon quoted Tsarnaev as once saying the U.S. uses the Bible as "an excuse for invading other countries."

"The fact that these terrorists were from overseas, living legally in our country for a period of time, and the fact that there was no federal intelligence or chatter prior to the marathon bombings demonstrates once again the Islamist terrorist threat to our country from within our borders,'' says Rep. Pete King, R-N.Y., chair of the House Homeland Security Subcommittee on Counterintelligence and Terrorism.

Sen. Tom Carper, who chairs the Senate Homeland Security and Governmental Affairs committee, says he hopes an investigation will provide answers to prevent a similar event. "I will do all that I can to help ensure that we learn from this tragedy and do what we can to prevent a similar situation from happening again so we can keep all Americans safe," Carper, D-Del., said.